With recent practical implementation of a blue light-emitting diode, studies are being aggressively made to develop a white light-emitting diode using the blue diode as the light emission source. The white light-emitting diode is lightweight, uses no mercury and has a long life, and therefore demands are expected to rapidly expand in the future. As for the method of converting the blue light of the blue light-emitting diode into white light, a method described, for example, in Japanese Unexamined Patent Publication (Kokai) No. 2000-208815 is most commonly performed, in which a coating layer containing a fluorescent material capable of absorbing part of blue light and emitting yellow light in the complementary-color relationship with blue light is provided. A mold layer for mixing the blue light of the light source and the yellow light from the coating layer is also provided in front of a light-emitting element which emits blue light. The coating layer heretofore employed is formed by coating a mixture of cerium-activated YAG (Y3Al5O12:Ce) powder and an epoxy resin on a light-emitting element. However, when a white LED is produced using a Ce-doped YAG, the light emitted contains a slightly blue-green tint and good white light cannot be obtained, because the fluorescent color of YAG:Ce is not completely complementary to blue.
On the other hand, a sialon-based phosphor activated by a rare earth element emits fluorescence of which the wavelength is longer than the fluorescence of Ce-doped YAG and is shifted to the red side, and therefore, when a sialon-based phosphor is used, a good white light-emitting diode can be produced using the blue light-emitting diode. The sialon-based phosphor itself is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2002-363554, but the sialon phosphor disclosed therein is a sintered body produced by a hot-press method. The method disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2000-208815 is widely employed as a production method of a white light-emitting diode, but in this technique, a phosphor powder is necessary. Therefore, in the case of a sialon phosphor produced by hot-pressing as in Japanese Unexamined Patent Publication (Kokai) No. 2002-363554, the phosphor needs to be strongly pulverized and formed into powder particles.
Consequently, we attempted a synthesis to obtain a powder sialon and found that a raw material composition containing a large amount of oxygen must be formulated to obtain a sialon phosphor powder. When a sialon is produced using a raw material composition containing a large amount of oxygen, the production of powder is relatively easy, but there is a problem in that the intensity of emission decreases.
We also confirmed that the obtained powder forms a large aggregated lump resulting from aggregation of sialon particles through a glass layer and cannot be completely pulverized by easy pulverization and becomes a powder containing large lumped particles (aggregated lump). Such a powder needs strong pulverization according to the purpose of use.
Thus, it could therefore be advantageous to provide sialon phosphor particles or a powder exhibiting high emission intensity in the region from ultraviolet to blue, and not requiring a strong pulverization for pulverizing a sintered body or a large aggregated lump, and a production method thereof.